The quality or power of transmitting heat and other rays of radiant energy with minimal absorption.
From Greek 'dia-' (through) + 'thermē' (heat) + '-ancy' (suffix denoting quality), an alternative technical term related to diathermancy used in physics.
Medieval scholars used the term diathermancy as they tried to understand why some materials seemed 'transparent to heat' long before they understood infrared radiation—they were actually observing quantum properties without the quantum mechanics.
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